Assessment of Somatosensory Function in Patients With Idiopathic Dry Eye Symptoms

Abstract

Somatosensory dysfunction likely underlies dry eye (DE) symptoms in many individuals yet remains an understudied component of the disease. Its presence has important diagnostic and therapeutic implications. To assess the integrity of nociceptive system processes in persons with DE and ocular pain using quantitative sensory testing (QST) techniques applied at a site remote from the eye. A cross-sectional study conducted at Miami Veterans Affairs Hospital included 118 individuals with a wide variety of DE symptoms and signs. The study was conducted from October 31, 2013, to January 28, 2016. Individuals completed questionnaires regarding ocular symptoms (5-Item Dry Eye Questionnaire [DEQ5], Ocular Surface Disease Index [OSDI], and Neuropathic Pain Symptom Inventory modified for the eye [NPSI-E]), psychological status, and medication use and underwent an ocular surface examination. The QST metrics included measures of vibratory and thermal thresholds and cold and hot pain temporal summation (surrogate measures of central sensitization) on the forearm. Correlations among DE and ocular pain symptom severity with QST metrics measured on the forearm. The OSDI score ranges from 0 to 100, with 100 indicating the most severe DE symptoms. The DEQ5 score ranges from 0 to 22, with the highest score indicating the most severe symptoms, and the NPSI-E score ranges from 0 to 100, with the highest score indicating the most severe symptoms. Psychological state was measured with the 9-item Patient Health Questionnaire, the PTSD Checklist-Military Version for PTSD, and the Symptom Checklist-90 for anxiety. Of the 118 patients who participated in the study, 105 (88.9%) were men (mean [SD] age, 60 [10] years), and a mean of 41% had PTSD, 10% depression, and 0.93% anxiety. Using stepwise linear regression analyses, significant associations were identified between overall DE symptom severity and posttraumatic stress disorder scores and tear breakup time (DEQ5 model: R = 0.54; OSDI model: R = 0.61, P < .001). All other variables (ie, demographics, comorbidities, medications, tear film factors, and QST metrics) dropped out of these models. When specifically considering neuropathic-like qualities of DE pain, however, anxiety and hot pain temporal summation at the forearm explained 17% of the variability in ocular burning (R = 0.41; P < .001), and PTSD score, tear breakup time, and hot pain temporal summation at the forearm explained 25% of the variability in sensitivity to wind (R = 0.50; P < .001) and 30% of the variability in total NPSI-E scores (R = 0.55; P < .001). Our findings demonstrate that neuropathic-like DE pain symptom severity correlates with quantitative measures of pain sensitivity at a site remote from the eye. This result provides additional evidence that DE symptoms are not only manifestations of a local disorder but also involve somatosensory dysfunction beyond the trigeminal system.